In many of the world's countries, there is a certain interest in being able to monitor telecommunication processes and contents for subscribers under particular circumstances. In this case, by way of example, telephone calls need to be monitored, but emails, short messages (known as SMS), faxes etc. also need to be read. Legal constraints and principles for telecommunication monitoring are then usually stipulated in various national acts and/or decrees in the respective countries—such as in a police act, in the code of criminal procedure, in a constitutional act, in a telecommunication monitoring decree, etc. These acts and decrees rule that the telecommunication monitoring may be performed only for the purpose of criminal prosecution and can be arranged only by a judge, for example.
The technical expression “lawful interception” (LI) denotes a security process in this context. By this means, an operator of a telecommunication network or a provider of telecommunication services (e.g., Internet provider, internet protocol (IP) telephony provider, etc.) allows a national office or authority authorized for monitoring (e.g., police, customs tracing, etc.), which is generally also referred to as a law enforcement agency (LEA), to access telecommunication processes and contents (e.g., telephone calls, email traffic or fax traffic, call-related data such as dialed telephone number, telephone number of an incoming call, etc.) for a particular subscriber. Lawful interception usually allows the nationally authorized office or authority to enter particular calls and thereby to eavesdrop on/monitor the telecommunication processes of a particular subscriber which are taking place therein.
Usually, what is known as a lawful interception interface for a data transmission between the telecommunication network operator or telecommunication service provider and the monitoring office or authority is set up for this purpose in the telecommunication network. In an instance of monitoring, this lawful interception interface is then used to transmit, by way of example, data—such as call content, fax data, call-related data, content of emails or short messages—from the telecommunication network to a monitoring device of the legally authorized office or authority, usually in real time.
To make it easier to implement lawful interception and in order also to allow cross-border—e.g., Europe-wide—monitoring of telecommunication processes and contents, standards and technical specifications have been developed for lawful interception and the relevant interfaces—examples being ES 201 671 Telecommunications Security; Lawful Interception (LI); Handover Interface for Lawful Interception of Telecommunications Traffic; TS 101 232 Telecommunications Security; Lawful Interception (LI); Handover Specification for IP delivery, etc., which have been published by the Technical Committee on Lawful Interception (TC LI) of the European Telecommunications Standards Institute (ETSI). These standards and technical specifications for lawful interception which has been published by ETSI are used primarily in Europe, in large parts of Asia and in some cases also in Australia. These standards provide a very detailed description not only of the architecture of a system and the interfaces for lawful interception but also of telecommunication-network-specific protocol requirements and procedures which are necessary in order to transmit data for the telecommunication processes of a monitored subscriber from the telecommunication network operator or provider of telecommunication services to the office or authority legally authorized for monitoring.
In the United States, the principles for lawful interception have been defined in what is known as the Communications Assistance for Law Enforcement Act (CALEA) and have been supplemented by publications from various committees of the Alliance for Telecommunications Industry Solutions (ATIS)—such as PTSC LAES (Packet Technologies and Systems Committee Lawfully Authorized Electronic Surveillance) or WTSC LI (Wireless Technologies and Systems Committee Lawful Intercept)—for various telecommunication network types, such as mobile radio networks, IP-based networks, etc.